


The Little Merman

by EclecticIsMyMiddleName



Category: Shingeki no Kyojin | Attack on Titan
Genre: Alternate Universe, Childhood Friends, Childhood Sweethearts, F/M, Friends to Lovers, Interspecies Relationship(s), Interspecies Romance, Interspecies Sex, Some Humor, The Little Mermaid AU, i will put a warning beforehand in the chapter summary, the mermaids in this au are less disney and more scary with claws and sharp teeth, there is an explicit sex scene in later chapters
Language: English
Status: In-Progress
Published: 2018-05-01
Updated: 2018-05-01
Packaged: 2019-04-28 22:51:29
Rating: Mature
Warnings: Graphic Depictions Of Violence
Chapters: 1
Words: 3,419
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14459544
Author URL: https://archiveofourown.org/users/EclecticIsMyMiddleName/pseuds/EclecticIsMyMiddleName
Summary: Eren and Armin dreamed of seeing the Surface World ever since they were little, but merfolk and humans are forbidden from interacting. So what will Eren do when he meets a human princess and falls for her?Loosely based on the Disney 1989 movie.





	The Little Merman

**Author's Note:**

> For clarity, Armin, Eren, and Mikasa are about ten years old in the first chapter.
> 
> Chapter warnings for violence, death, near drowning, and references to human trafficking.

Miles outside of a hidden underwater city, two young merboys were playing. The brown-haired one was racing his friend, and the blond clearly had trouble keeping up.  
  
"Eren!" the blond cried, swimming as fast as he could to keep up with his friend. "Eren, slow down!"  
  
"Why don't _you_ catch up?" Eren joked, ducking behind a large coral. "Don't be such a guppy, Armin!"  
  
"I'm not a guppy!" Armin protested, pouting and sinking to the sandy ocean floor.  
  
Eren's laughter was cut off by a shadow passing over the sun above the water. Looking up, he saw something dark on the surface. "Whoa! What's that?"  
  
"What's what?" Armin asked, swimming to his friend. His blue eyes widened when he followed Eren's gaze. "That's a ship! From the Surface World!"  
  
"Let's go check it out!" Eren suggested, pushing off the coral and heading towards it.  
  
"No! Your Highness, please!" Armin protested, grabbing Eren's arm. Eren stopped and frowned at him. "It could be dangerous! Let me go; I'm expendable. You're the prince!"  
  
"Armin, what have I told you?" Eren replied, yanking his arm away and crossing his arms over his chest. "We're not in the city right now." He clutched the red sash he wore around his torso at all times. "Out here, my royal title means nothing!" His impatient tone softened as he added, "I'm just your friend, okay?"  
  
Armin sighed and nodded. "Okay, Eren."  
  
"And as your friend, I'm not gonna let you see what that is without me," Eren finished, resuming his swim to the ship. Armin shook his head and followed.  
  
Eren swam right up to it and began examining it, but Armin hung back a little.  
  
"Stop being a guppy, Armin!" Eren teased. "Ships don't bite!"  
  
"I can observe it just fine from here, thank you!" Armin replied, crossing his arms. He ignored Eren when his friend stuck his tongue out at him.  
  
The ship was only about eight feet long and made of wood. Other than that, there wasn't much else to look at.  
  
"Kinda small, ain't it?" Eren remarked, knocking on the underside.  
  
"I think it's a rowboat," Armin said, daring to swim closer and putting his hand on the underside. "Humans have so many different kinds. It's hard to know for sure, even with the books we have back at the Grotto."  
  
"I wonder why it's not moving?" Eren wondered aloud, swimming to the edge of the rowboat. "Don't boats move?" He reached up and felt the air on his fingers as his hands broke the surface. He found the lip of the boat and pulled himself up enough to peek over the edge of the boat.  
  
His heart skipped a beat when he saw a human girl his age staring directly at him. Her eyes were steel-colored and lifeless as she sat stock still in her seat. Her hands were resting on her knees, rope binding them together. Her white gown was torn in some places. Despite the tears, the gown was clearly intricate and expensive. Eren felt fury ignite in him when he saw her lower lip was bloody.  
  
Two grown men sat in the boat with her. One of them was tall and lean while the other was short and squat. Neither of them looked very friendly.  
  
Luckily for Eren, neither of them seemed to notice he was there.  
  
"How much longer are we gonna wait for him?" the short one lamented, crossing his arms. "I hate the sea."  
  
"He said he'd meet us at sea so we wouldn't be followed," the tall one snapped. "God, you're more of a brat than _she_ is!"  
  
Eren bared his sharp teeth in a snarl, his temper flaring at the insult. He tensed when he felt a hand on his shoulder and glanced over to see Armin poking his head out of the water beside him. Armin opened his mouth to say something, but Eren put a finger to his lips.  
  
"I just wanna go home and get the money," the short one replied, shrugging. "The sooner I get home, the sooner I can forget what we did."  
  
Eren raised an eyebrow as his temper rose closer to its boiling point. He dared not breathe as he strained to hear every word.  
  
"Just be grateful we got the job," the tall one said, glancing at the girl. "And we didn't have to fight too hard to tie her up. Once her parents were dead, little thing just gave up." He scratched his scruffy chin. "Probably for the best she isn't much of a fighter. Otherwise, our buyer might have our asses for selling him more than he could handle."  
  
"I wish you wouldn't talk about the guy," the short one said, grimacing. "The less we talk about our buyer, the better I'll be sleeping tonight."  
  
"I know you don't like him," the tall one said. "Hell, I don't like him, either. But at least we got security in knowing our money's coming to us. It may not be my cup of tea, but at least our buyer is willing to pay handsomely for a docile little princess."  
  
Eren's claws scratched the wooden boat as he let himself sink back into the water.  
  
"What the hell was that?!" the short one exclaimed, tensing as he looked in the direction of the sound. "Was that the same thing that hit the boat earlier?"  
  
Not wanting to be left alone with these strange humans, Armin followed his friend below the surface.  
  
Eren swam down about ten feet, then faced the surface again. Predicting what he was about to do, Armin scrambled to swim out of the way as Eren swam straight up and shot out of the water. An eerie, inhuman screech erupted from his throat as he tackled the taller man.  
  
"Fucking hell?!" the man shouted right before Eren collided with him. The force of their collision forced both of them into the water.  
  
Armin's mouth fell open in shock as he saw Eren grip the human by the collar. The man kicked and twisted, struggling to free himself. Armin stayed out of his range and shouted, "Eren! Why are you doing this?!"  
  
"If no one else is going to fight, then I will!" Eren snapped, glaring daggers when the man stopped struggling to stare at him. His eyes flicked from Eren to Armin. His eyes grew wider as he realized what he was looking at two merboys that were speaking his language.  
  
"Don't kill him!" Armin begged, trying to keep up with Eren as the latter began swimming to the ocean floor. "I know he's not a good person, but there are laws against murder!"  
  
"This isn't murder, Armin!" Eren replied, his grip tightening on the man's clothes. "This is justice!"  
  
Eren's statement snapped the man back to reality and he resumed struggling. He tried to land a blow, but to no avail.  
  
Once far enough down, Eren let him go and slashed at him.  
  
"Die!" Eren shouted, baring his teeth and swinging at him. The claws on his webbed hands sliced the man's stomach on the first swing. "This is what you beasts deserve!" His claws sliced his face on the third swing, and finally, his throat on the last swing. "This is what you get for being what you are!"  
  
"Eren!" Armin cried, cowering beneath the boat. Unable to take the sight of blood, Armin had swam back up to the boat and seen the smaller man grab the girl. "Eren! The other one is hurting the girl!"  
  
Growling, Eren shot back up to the surface and pulled himself up onto the edge of the boat. A second later, he dropped back into the water just as the gun in the man's hand went off.  
  
"Dammit!" Eren swore, letting himself sink down again. While Eren swam down into the depths for his next attack, Armin poked his head above the surface. He rose above the water just enough so that the boat would hide him.  
  
"I know you're there!" the short man shouted, holding the girl by the binds around her wrists. "You probably killed my partner, so I know I'm your next target! But I'm warning you: try to kill me, and _she_ gets the next bullet!"  
  
Eren shot out of the water again, hitting the man from behind. Armin covered his ears as the gun went off again. Eren, the man, and the girl went tumbling into the water.  
  
"Oh, no!" Armin cried as he ducked beneath the surface.  
  
Eren grunted as the man landed a kick to his stomach. Exposing his sharp teeth in a growl, Eren lunged at him. He slashed wildly and managed to drag his claws across the man's chest.  
  
Preoccupied with his opponent, Eren didn't see the air bubbles coming from the girl's mouth.  
  
"She can't breathe!" Armin exclaimed, rushing to the girl's side. Taking her bindings to his teeth, he gnawed her free. Once the rope was severed, she started to sink. As her body went limp, Armin cried, "No, no, no!"  
  
Eren slashed at the man again, and his claws went straight through his neck. He watched his corpse start to sink before turning his attention back to the girl. Seeing Armin struggle with her, he rushed to her and helped Armin carry her to the surface.  
  
Eren let go of her long enough to pull himself into the rowboat before grabbing her. Eren pulled while Armin pushed and together, they hauled her onto the boat.  
  
"Is she okay?" Armin asked, peeking over the side while Eren cleared her sopping hair away from her face.  
  
"I don't know," he mumbled, leaning down to put her ear to her chest. Her heart beat was faint and panic flooded him. "No!" He took her by the shoulders and shook her. "Wake up! You can't die after all that! Wake up! Wa-" He let go abruptly when she started coughing up salt water.  
  
"Ew," Armin remarked, wrinkling his nose as the girl rolled over to empty the salt water from her stomach. Eren shot his friend an annoyed look before looking back to the girl.  
  
He hesitated a moment before reaching out and rubbing her back while she retched. "Hey, you're gonna be okay now. We saved you from those monsters."  
  
When her breathing had returned to normal, she turned and slowly looked up at him. Her red-rimmed eyes were glistening with tears. Her cheeks were red and blotchy.  
  
"You...saved...me?" she asked, her voice hoarse. She coughed into her hand and wiped her mouth with the back of her hand. Pulling her legs to her chest and hugging herself, she stared at him with wide eyes. "You're not...human."  
  
Eren shook his head. "I'm Eren." He gestured to Armin, who gave a shy wave. "That's Armin. What's your name?"  
  
"You speak my language?" the girl marveled, the fear in her melting into wonder.  
  
"Well, yeah," Eren replied, shrugging. "All my people can speak your language. Now, what's your name?"  
  
"Mikasa Ackerman," she replied, sitting up straighter. "Princess of The Walls." A sudden gust of wind rolled over them and she shivered. Eren's hands flew to the royal sash around his torso.  
  
"Here, this should keep you warm," he said, removing the red material and running a hand over the fabric. In an instant, the fabric was dry and he wrapped it around Mikasa's neck like a scarf. "There. Now, tell me: what are The Walls?"  
  
His question went unanswered as Mikasa pointed behind them. "Look! It's the Royal Navy!"  
  
Eren whipped around and saw she was right: three large battle ships were heading their way. They all bore the same flag that featured the heads of three goddesses on shields.  
  
"I've got to go!" he exclaimed, turning back to her. "My kind aren't allowed to make contact with humans!"  
  
Mikasa's eyes brimmed with tears and her voice was so quiet, Eren almost didn't hear her. "Will I see you again?"  
  
"I don't know," Eren replied, ignoring Armin's hand tugging on the fin on his forearm. "But I hope so."  
  
Mikasa leaned forward before Eren could react and pressed a kiss to his cheek. Eren flushed and brushed his fingers against the spot where she had kissed him. Meanwhile, Armin was pulling hurriedly on his arm.  
  
"C'mon, Your Highness!" Armin exclaimed, his eyes fixed on the incoming battle ships. "We must go now!"  
  
Eren snapped back to reality. He and Armin plunged into the water moments before the battle ship reached the rowboat. The two of them watched from afar as royal naval officers helped the princess to safety.  
  
"King Grisha is gonna kill you when he finds out you saved a human," Armin said, wringing his hands. "And then he'll kill me for helping!"  
  
"Then it's a good thing my father won't find out."

 

* * *

 

"You what?!" the king shouted, banging his fist on the armchair of his throne. "You went up to the surface again, didn't you?" King Grisha rose from his throne with an exasperated sigh. "How many times must we go through this? Humans are dangerous. They bring nothing but trouble!"  
  
"But this human was just a girl!" Eren protested, his temper flaring as he raised his voice. "There wasn't time to get help! Those humans were going to sell her!"  
  
"What humans do with one another is none of our concern!" the king snapped, thumping a fist to his chest. "We worry about our _own_ kind!"  
  
"How can you say that?!" Eren shouted, balling his fists. "She's just a child-!"  
  
"Enough arguing, Eren!" King Grisha interrupted sharply, swimming up to his son. "Be content in knowing you saved her, and forget about her. Humans are dangerous. Don't you remember how they killed your mother?"  
  
At the mention of his mother, Eren's chest tightened and he felt his eyes sting with budding tears.  
  
"I won't lose you like I lost her," King Grisha continued, putting his hands on his hips. "So I am never - _never_ \- to hear of you going to the surface again! You are going to stay right down here where you belong! Is that clear?"  
  
Eren ducked his head to hide the angry tears spilling from his eyes and mixing with the salt water around him. "Fine!" He bit his lip to muffle a sob and kept his eyes fixed on the ocean floor. "I'm sorry I disobeyed you. I know you hate the Surface World, but I didn't know how else to save her!"  
  
King Grisha's expression softened and he pulled his son into a hug. "Son, I understand why you helped her. She was innocent and defenseless. I know how hard it is to ignore the instinct to protect someone like that." He cupped the back of his son's head and tilted Eren's gaze up at him. "But you must be careful. Do you think I want to see you snared on some human's hook? Or caught in one their nets?"  
  
Eren had been very young when human sailors killed his mother, Queen Carla, but that day was burned into his memory like a brand. He knew he'd never forget his mother struggling after being caught in a net. After trying to gouge out the eyes of a sailor, they had speared her with a harpoon.  
  
Eren shut his eyes against the memory and hesitated before hugging his father back. "I'm sorry, Dad. I didn't mean to worry you, but I just wanted to help her."  
  
"I know, son," his father replied, patting him on the back. "I know."  
  
"I probably won't see her again, anyway."

 

* * *

 

Mikasa sat on the couch by the window, pulling the comforter tighter around her as she stared out into the night. She could see Wall Sina in the distance, but in her mind, she was looking at the ocean. She tried to picture the moonlight dancing on the surface of the water.  
  
The door opened and interrupted her daydreaming, but she didn't turn around. She already knew who it was by the scent of black tea wafting towards her.  
  
"Hello, Uncle Levi," she said, glancing at her uncle as he sat in the chair in the corner of her room.  
  
"Hello, little Mikasa," he greeted, his voice even as usual. His expression never wavered from its typical blank slate as he asked, "Do you realize how lucky you are to be alive right now?"  
  
Mikasa nodded and took the cup of tea he handed her. She blew on it to cool it before taking a sip.  
  
"It was chaos trying to find you after you were taken," he continued. The only outward sign of his anger was his grip on the armchair tightening. "In my haste to avenge your parents' deaths, I killed the third suspect. I should have left him alive for questioning."  
  
Mikasa kept her gaze on the tea cup in her hand, but her eyes were glazed over. She sniffled and her uncle's grip on the armchair loosened.  
  
"I'm sorry," he said, softening his voice in the way he reserved only for loved ones. "I should have realized your parents are the last thing you want to think about right now. My condolences about their deaths. They will be missed."  
  
Mikasa set her cup down on the window sill and looked over at him. Though she had always been adept at concealing her emotions, her family could read her like a book. Levi knew by the subtle tremble of her lower lip and the faint red tinging her cheeks that she was about to start crying.  
  
"C'mere, little Mikasa," Levi said, holding his arms out to her. Without a word, she crawled off the couch and he helped her onto his lap. Wrapping his arms around her, he added, "I'm here for you. My wife and I will take you in, and raise you like our own. I promise you won't be alone." She clutched the fabric of his shirt in her hands and pressed her cheek to his chest. "But comforting you is not the only reason I came here tonight."  
  
Mikasa swallowed against the lump in her throat and peeked up at him. "What is it, Uncle?"  
  
"The Council that advised your parents have appointed me King Regent. It's only until you are old enough to be crowned queen," he explained, rubbing her back as Mikasa wiped the tears from her eyes. "On your twenty-first birthday, I will step down so you can rule."  
  
"How do I know I'll be a good queen?" she asked, her head beginning to ache as she strained to keep the tears from building again.  
  
"We will teach you how," he replied. "Besides, you will have the lessons your parents taught you. But none of that will matter if you don't believe in yourself."  
  
Mikasa nodded and rested her cheek against his chest again. Closing her eyes, the events of the day replayed behind her eyelids.  
  
The day had started so well. Her mother had taught her a new stitching technique that morning. Her father had promised to show her how to hunt on his next hunting trip. Their plan to spend the day among the nobility was supposed to inspire a sense of community between the royal family and the people of The Walls.  
  
_If only we had known,_ she thought, feeling her chest tighten and her eyes sting. The pain in her chest alleviated a little as she realized she wouldn't have met Eren and Armin if her parents hadn't been murdered. _At least I made two new friends._  
  
"What's on your mind, little Mikasa?" Levi asked, snapping her out of her deep thought. "You're quiet. Well, quieter than usual. Thinking about those boys that saved you?"  
  
Mikasa blushed and buried her nose in her scarf. "You don't believe me, do you?"  
  
"Don't worry, I believe you," he replied. "There are many things in this world we can't be sure of. I say the best course of action is to follow your gut. If your gut tells you they were real, then they were."  
  
Almost no one had believed her when she explained that two merboys had saved her from traffickers. Her already-broken heart had cracked further as everyone from the ship captain to the servants insisted she had imagined them. Knowing at least one person believed her chased away some of the loneliness that threatened to swallow her up.  
  
Mikasa brushed her fingers against the scarf she wore around her neck. "I hope I see them again."

**Notes for the Chapter:**

> I have a twitter if you wanna go follow me there! :)  
> Twitter: https://twitter.com/EclecticWrites   
> My handle is @EclecticWrites.


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